Organic light emitting diode (OLED) display apparatus has many advantages, such as low power-consumption, high color saturation, wide viewing angle, ultra-thin structure, and flexible displaying ability, etc. Thus, it has become a mainstream technology in the display field.
FIG. 1a illustrates a general structure of an OLED. As shown in FIG. 1a, the OLED includes a substrate 001, an anode 002, a light-emitting layer 003, and a cathode 004 sequentially formed on the substrate 001. When a voltage is applied between the anode 002 and the cathode 004 to generate a current, the electrons in the cathode 004 and the holes in the anode 002 may combine within the light-emitting layer 003 to form excitons. The excitons activates the organic material in the light-emitting layer 003 to emit light.
Further, as shown in FIG. 1b, the OLED also includes a hole injection layer 005; a hole transport layer 006, and an electron barrier layer 007 formed between the anode layer 002 and the light-emitting layer 003. Further, the OLED also includes an electron barrier layer 008, an electron transport layer 009 and an electron injection layer 110 formed between the light-emitting layer 003 and the cathode 004.
Thus, as shown in FIG. 1a and FIG. 1b, the OLED includes a plurality of layer structures. Light emitting from the light-emitting layer 003 is scattered and absorbed repeatedly during the light transport process in the plurality of layer structures. The light energy can be significantly loss due to a light wave-guide effect during the light transport process. Thus, there may be only a small amount of light emits from the OLED; and the luminous efficiency may be relatively low. Therefore, the external quantum efficiency of the OLED may be relatively low.
According to the light-emitting mode, OLEDs may be categorized to top-emitting OLEDs and bottom-emitting OLEDs. The bottom-emitting OLED emits light from the substrate side; and the top-emitting OLED emits light from the top side. The cathode of the top-emitting OLED is often made of metal material; it may block a certain amount of light; and it may reflect light. Thus, the cathode of the top-emitting OLED may have to be relatively thin. If not, the external quantum efficiency of the top-emitting OLED may be substantially low; and the image quality and the display effect may be significantly impaired.
Therefore, how to improve the external quantum efficiency of OLED devices; and to reduce the luminous efficiency loss caused by the light wave-guide effect has become a demanding issue in the field of the display technologies.
The disclosed methods and systems are directed to at least partially alleviate one or more problems set forth above and other problems.